Electric current interchange contact



APril 1963 R. w. BETHKE 3,087,038

ELECTRIC CURRENT INTERCHANGE CONTACT Filed Oct. 19, 1959 3 Sheets-Sheet1 INVENTOR. Qwand 24. Beth k:

flttorney- April 23, 1963 R. w. BETHKE ELECTRIC CURRENT INTERCHANGECONTACT 3 Sheets-Sheet 2 JMMW mixn r W a F M Zr/l/l? B Filed Oct. 19,1959 April 23, 1963 R. w. BETHKE ELECTRIC CURRENT INTERCHANGE CONTACT 3Sheets-Sheet 3 Filed Oct. 19, 1959 8 M L my m 1 Z X 3,087,038 PatentedApr. 23, 1963 3,087,038 ELECTRIC CURRENT INTERCHANGE CONTACT Raymond W.Bethkc, 4459 S. New York Ave, Cudahy, Wis. Fiietl Oct. 19, 1959, Ser.No. 848,383 19 Claims. (Cl. 2u0166} This invention relates to electriccontacts and more particularly to a means for transferring current oflarge magnitude between conductive components which coact slidably orrotatably in electrical apparatus.

This is a continuation-in-part of copending application Ser. No.505,293, filed May 2, 1955, and which is now abandoned.

In circuit breakers, switches and other electrical devices, it is oftennecessary that current be conducted between components which aremechanically related but free to exercise a predetermined swinging orsliding movement with respect to each other. For example, in a circuitbreaker an elongated rod like contact may be arranged for sliding intoand out of electrical engagement with a fixed contact so that currentmay be transferred during the conductive period from the sliding contactto its guiding member. In a circuit interrupter it is common to transfercurrent from a swinging arm to an arm support through a poorlyconductive hinged joint, and also between a stationary contact block andcontact lingers slidably received therein. These are but a few of theinstances where it will be evident to those versed in the art that ahigh resistance junction may develop between movable parts which wouldmanifest itself in the form of heat and excessive voltage drop acrossthe apparatus and which results in rapid wear The prior art demonstratesa variety of means for mitigating the aforementioned affects such as, byparalleling the high resistance junction between movable parts by meansof flexible shunts, cam and follower arrangements, and direct actingwiping contacts. Moreover, in the hinge joints various means ofachieving high pressure contact have been used: for example, hingedparts may be biased into high pressure relation in an effort to minimizecontact resistance between them.

Despite the abundance of known current interchange means, none of thesedevices are fully satisfactory because they frequently deteriorate afterprolonged use, and because they are costly, intricate and difiicult toincorporate where space limitations are an important factor.

A general object of this invention is to overcome the above indicateddefects in the prior art by providing a novel and eliicient means fortransferring current through rotatable and slidable joints betweenmovable components of electrical apparatus.

A principal object of the invention is to provide a contact which ottersonly infinitesimal mechanical rolling friction between components.

Other more specific objects are: to provide a current transfer contactwhich is simple in form and easily manufactored and installed; toprovide a contact which is endowed with inherent ability to compensatefor wear, it any; to provide a contact which may be conveniently gangedor stacked for accommodation of large magnitude currents; and, toprovide a contact which is free floating and self-adjusting therebyeliminating sizing or binding of the parts.

Another important object is to provide a current transfer contact whichincreases its bearing pressure through self-generating electromagneticefiects, when subjected to inordinate current flow.

These and other objects of the invention will become apparent from thedetailed description of the invention taken in view of the accompanyingdrawings in which:

FIG. 1 is an elevational view, partly in section, of a circuit breakercontact assembly incorporating one embodiment of the instant invention;

FIG. 2 is a sectional view, taken along lines 2-2 of FIG. 1;

FIG. 3 is an elevational view, partly in section, of an alternative formof the invention;

FIG. 4 illustrates how other embodiments of the instant invention may beincorporated in a circuit interrupter;

FIG. 5 is a sectional view of a circuit breaker contact embodying theinstant invention;

FIG. 6 is a view taken along lines 6-6 of FIG. 5;

FIG. 7 illustrates another application of the rolling currentinterchange spring according to the instant invention; and

FIG. 8 is a view taken along lines 9-9 of FIG. 7.

In general terms, the invention comprises a current interchange meanswhere current is transferred between relatively movable members throughthe agency of a helically wound spring. The springs are disposed in agroove in one of the members whose dimension in the direction ofrelative movement is substantially greater than the helical diameter ofthe springs. During relative movement between the conductive members,the spring is caused to roll in said groove so that only rollingfriction is encountered at the current interchange joint. As a result,the amount of force necessary to move the relatively movable members issubstantially reduced and the amount of wear experienced is negligible.In a more specific form of the invention the depth of these grooves isless than the helical diameter of the springs so that all convolutionsthereof are inclined, whereby contact hearing pressure is obtained fromtheir tendency to straighten out. For higher values of current aplurality of springs may be utilized having their convolutions inclinedin opposite directions relative to springs adjacent thereto to preventintermingling of their convolutions. In order to achieve rollingfriction during the entire period of relative movement, the width of thegroove is made equal to the sum of the diameters of all the springsutilized plus one half the distance between the limits of said relativemovement.

Referring to the drawings in greater detail, FIG. 1 shows an elongatedrod-like contact 1, of a suitable conducting material such as copper,arranged for executing rapid movement into and out of electricalengagement with a stationary contact 2. Although means for effectingrapid longitudinal travel of rod 1 are not shown, it may be assumed thatany well known driving means is attached to rod 1 at its upper end 6 forthis purpose. In practice, suitable arc extinguishing means would beprovided in the vicinity of contact 2 for confining the are formedthereabout during a circuit interrupting operation but this structure isomitted for the sake of brevity.

In connection with FIG. 1, it may be assumed that the objective is totransfer current from movable rod 1 to a stationary terminal assembly 8to which a line wire (not shown) is attached, the transfer beingeffected through the agency of a current interchange spring 17. Inclosed circuit position, rod 1 is received by the stationary contact 2which may take any well known form but is shown here comprising aconductive base 5 for attachment to a line wire (not shown). Flatupstanding resilient springs 4 are mounted on base 5 and are providedwith copper tungsten arcing tips 3. Conductive terminal casing 8 may besecureiy mounted in a circuit breaker or other electrical apparatusthrough the agency of bolt holes 9 formed in an integral supportingflange 10.

Additional guidance for rod 1 is obtained by passing it through aclearance hole 12 in the bottom of terminal housing 8 and a bushing 14shown threaded into housing 8 and provided with an aperture 13. It isnot intended that appreciable current be transferred from rod 1 to theinner walls of apertures 12 and 13, their fit with rod 1 being such asto allow free rotation or sliding thereof. While rod 1 is shown to havea circular cross section it will be understood that it may also bepolygonal in cross section without departing from the terms of theinvention.

According to the invention current transfer is accomplished by means ofa current pick up coil spring 17 which resides in a circular channel orgroove 18, formed in terminal 8 so that the spring wraps around andbears against rod 1 like a closely surrounding toroid, the outerdiameter of which is in current exchanging contact relation with theperipheral walls 19 of channel 18 and whose inner periphery bears on rod1.

By reference to FIG. 2 it will be apparent that each successiveconvolution of spring 17 is inclined at an angle with respect to theradius of rod 1 and its own helical axis thus accounting for the factthat the spring fits into a channel 18 which has a smaller width thanthe diameter of the individual spring convolutions. When the spring isdisposed in this position, contact pressure on rod 1 and channel wall 19is derived from internal stress which tends to right the convolutions toan untilted position so that each convolution has the effect of oneforce member interposed between two fixed points. Because spring 17 isinclined, this force is vertically divisible into two components withrespect to the surface against which it bears, the first being normal tothe periphery of rod 1 and the second being tangential thereto. This isdue in part to the normal contact force varying in magnitudesubstantially as the cosine of the inclined angle when that angle hasits vertex where the outer periphery of the convolution makes pointcontact with wall 19 and is measured from the face of the convolution toa radius extending to the same point from the center of rod 1. A tiltangle from 30 to 45 degrees has been found to yield the best results.This suggests Why the width of channel 18 is not extremely critical inthe invention, since the stresses set up in the spring 17 are notlinearly related to the strain created by the channel walls actingthereon; rather, they vary nonlinearly as does the sine function. Hence,a few thousandths of an inch of variation in channel Width produces onlya fractional difference in the bearing pressure exerted by spring 17.

It will be understood by those skilled in the art that the proportionsof spring 17 are determined by the mag nitude of the current to betransferred and the type of material utilized. For proper functioning ofthe tilted spring transfer contact 17, the circumference of rod 1 shouldbe greater than the length of spring 17 when it is closely wound andextended in a straight axial direction to prevent interference betweenadjacent convolutions. This insures that spring 17 will fit into channel18 when the former is inserted with its convolutions tilted.

After spring 17 is wound, it is preferable, although not absolutelynecessary, that its free ends by joined to form a. circular or toroidalunitary spring having an inside opening somewhat smaller than thediameter of rod 1. This may be accomplished by directly welding the endsthereof, by joining the ends in a sleeve and staking them together, orby merely intertwining the last few turns of each end. Spring 17 mayalso be wound with the convolutions having a preset angular inclinationwhich facilitates installation and controls its internal stresses.

It should be noted that the axial width of channel 13 in FIG. 1, exceedsthe helical diameter of the spring 17. The longitudinal freeplay thuscreated allows spring 17 to roll in the axial direction of rod 1, whenthe rod is caused to move axially, until the spring stops againstbushing 14 or channel bottom 20, depending upon the direction ofmovement. Thereafter, as the stroke of rod 1 continues, it merely slideswithin the spring 17 toroid. Rolling of the spring current exchangemeans is akin to mounting the rod 1 on ball bearing guides wherebystatic friction is reduced and a correspondingly rapid acceleration ofthe moving contact 1 is facilitated.

It should be understood that the phrases helical diameter and diameterof the spring eonvolutions" or diameter of the convolutions or diameterof the spring, wherever used in this specification or the appendedclaims, means the outer diameter of the spring when wound as an untiltedhelix. It should be further understood that the width of the groove,means its dimension parallel to the direction of relative movement whileits depth, means its dimension perpendicular to said direction.

In an alternate form of the invention shown in FIG. 3 the width ofchannel 18 is substantially equal to one-half the stroke of rod 1 plusthe helical diameters of springs 17 and 17'. This allows currentinterchange springs 17 and 17' to roll during the entire stroke of rod 1because a body rolling on a cylinder or ball travels approximately twiceas far as the cylinder itself. As a result, not only is very littlestarting friction encountered, but the friction remains at a small valueduring the entire contact opening and closing operation. The secondcurrent interchange spring 17' is shown in FIG. 3 to illustrate that forlarge current applications a plurality of springs, may be used. If thesprings 17 and 17' are inclined in the same direction an annular spacermember 21, should be utilized. Spacer 21 is not necessary, however, ifthe springs are inclined in opposite directions to prevent interminglingof their convolutions. When additional springs are used the width of thechannel or cavity 18 should be increased by the diameter of each suchadditional spring so that they will be free to roll through the entirestroke of rod 1. It will be appreciated that the current interchangemeans shown in F165. 1 and 3 may also be utilized to transfer currentbetween reciprocating members.

In circuit breakers utilizing butt type contacts as shown in FIG. 4, ithas been determined that in order to prevent the contacts from blowingopen and/or subsequently Welding, one contact finger per to thousandpeak instantaneous ampcres is required. The exchange of current betweenthe moving arm and the stationary contact 32 is further complicated bythe necessity for over-travel required to allow a latch or toggle tomove over its set position and relax back against the stop so that themovable contact 36 may be held in closed position. In addition, slightchanges in the adjustment of the operating mechanism should not affectthe contact pressure between the fixed and movable contact members.

The contact mechanism shown in FIGS. 4-6- satisfies each of theserequirements. In general terms the contact structure includes aplurality of contact fingers 34 reciprocably mounted in a contact block35. Current is transferred between the contact fingers 34 and contactblock 35 by means of current interchange springs disposed therebctweenand lying with their helical axes substantially perpendicular to a planecontaining the direction of movement of said contact fingers.

More specifically, contact block 35 includes three spaced apartplatelike sections 38, 39 and 40 which are joined by an end portion 41and which define, with end plates 45, a pair of parallel rectangularslots or cavities 43 and 44.

Each of the contact fingers 34 includes a head portion 48 and a bodyportion 49 having a substantially H- shaped cross section. The lateralsurfaces of the upper and lower arms 50 and 52 respectively, of eachbody portion 49, slidably engage the upper and lower walls of theirassociated cavities 43 and 44. The space between these upper and lowerarms provides a spring channel 54 for receiving current interchangesprings 36. As can be seen in FIGS. 4 and 5 the individual springchannels 54 of each contact finger 34 are in substantial registry sothat each current interchange spring may overlay all of the contactfingers.

As seen in FIG. 5, the depth of each of the spring channels 54 is lessthan the helical diameter of the interchange springs 36 so that eachspring is obliged to lay over at an angle dictated by the depth of saidchannel. The tendency of the spring to assume its unstressed shapeprovides contact pressure between the walls of cavities 43 and 44 andthe inner surface 55 of spring channels 54. If a plurality of springsare employed in any spring cavity, adjacent springs are laid over inopposite directions, as shown in FIG. 6, to prevent mingling of theindividual convolutions.

A biasing spring 58 is provided to urge each of the contact fingers 34against stop plate members 59, disposed at the front of the contactblock 35, and each of which overlaps slightly the openings of thecontact finger cavities. Springs 58 provide contact pressure between thecontact fingers 34 and the movable contact 30 and also allow for theover-travel of said movable contact mentioned above. As a result of thisover-travel, the contact fingers 34 are forced further into theirrespective contact finger cavities against the biasing force of theirindividual contact pressure springs 58. During this movement currentinterchange springs 36 provid a rolling connection between contactfingers 34 and plate portions 38, 39 and 40 of contact block 35. As aresult only a small frictional force is encountered by movable contact30 so that rapid closing of the contacts is not inhibited and the wearon the movable parts of fixed contact 32 is relatively small. Inaddition, this novel current interchange means allows each of thecontact fingers 34 to move individually so that a good contact can beachieved between each of the contact fingers and the movable contact 39.Here again, the width of each of the spring channels 54 is equal toapproximately one-half the amount of contact finger travel plus the sumof helical diameters of each contact spring utilized so that onlyrolling friction is encountered.

FIGS. 7 and 8 illustrate how the rolling spring contact principle can heapplied to relatively rotatable members. By way of example, theembodiment of FIGS. 6 and 7 will be discussed in relation to thetransfer of current between switch arm 60 of movable contact 30 and thestationary conductive member 62 upon which it is rotatably mounted bymeans of a pivot pin 63. Conductive member 62 is substantially U-shapedwith its legs 64 and 65 joined at one end by cross piece 66 and at theirother by a cylindrical conductive sleeve 67. Similarly, each of the arms68 and 69 of rotatable contact 30 is joined at its pivotal ends bycylindrical conductive member 70 which is slidably received withinsleeve 67. A plurality of spaced apart substantially parallel channels74 are formed in the surface of cylindrical member 70 for receivingcurrent interchange springs 75. Here again, the depth of recesses 74 isless than the diameter of springs 75 so that the convolutions thereofare forced to lay over whereby contact pressure with cylinder 70 andsleeve 66 is provided. The arcuate width of each of the grooves 74 isapproximately equal to one half of the arc intercepted by the rotationalangle of switch arm 60 plus the diameter of springs 75 so that only arolling friction is encountered as switch arm 60 oscillates between openand closed position.

The number of grooves 74 and springs 75 employed in cylindrical member70 is determined by the magnitude of the current to be transferred. Aplurality of springs 75, each having an angle of inclination dilferentfrom adjacent springs, may also be used in each groove where largecurrents are involved.

For purposes of illustration, each of the embodiments shows the springreceiving groove or channel formed in a particular one of the members,but those skilled in the art will understand that it also may be formedin either member or that a portion may be formed in both members.

Also, while each of the embodiments has been discussed with respect toparticular types of interchange structure, these are merely intended asexamples. Accordingly, it is intended to cover in the appended claims,

the rolling spring principle of current interchange in all types ofapplications.

I claim:

1. In electrical apparatus, current interchange means comprising a pairof relatively movable conductive members, means associated with saidmembers for providing an elongate channel having its open side disposedtoward one of said members, a helical spring contact disposed in saidchannel, the normal distance between said members and across saidchannel being substantially uniform, said distance being less than theoutside helical diameter of the convolutions of said spring to inclinesaid convolutions at an angle relative to the helical axis of saidspring so that the resiliency of said spring normally holds saidconvolutions in firm electrical contact with said mem bers, the width ofsaid channel in the direction of relative movement exceeding thediameter of said convolutions so that said spring rolls during saidmovement whereby rolling friction is encountered between said membersand said spring contact.

2. In electrical apparatus, current interchange means comprising a pairof relatively movable conductive members, means associated with one ofsaid members to provide an elongate channel having an open side disposedtoward the other member, a helical spring contact disposed in saidchannel, said channel and said spring being so arranged that a planecontaining the helical axis of said spring is perpendicular to thedirection of relative movement, the normal distance between said membersand across said channel being substantially uniform and less than theoutside helical diameter of the convolutions of said spring so that theplanes of said convolutions are inclined at an angle relative to itshelical axis, the resiliency of said spring normally holdingsubstantially all of said convolutions in firm electrical contact withsaid members, the dimension of said channel in the direction of relativemovement exceeding the diameter of said convolutions so that said springrolls during said relative movement whereby rolling friction isencountered between said members and said spring contact.

3. In electrical apparatus, current interchange means comprising a pairof conductive members, one of said conductive members being relativelyfixed and the other being movable between first and second positions,means integrally formed with one of said members to provide an elongatechannel having its open side disposed adjacent the other member, helicalspring contacts disposed in said channel, the depth of said channelbeing substantially uniform and less than the outside helical diameterof said springs so that the convolutions thereof have their planesinclined at an angle relative to its helical axis, whereby theresiliency of said springs normally holds said convolutions in uniformlyadvancing spiral relation with each other and maintains saidconvolutions in firm electrical contact with said members, the width ofsaid channel in the direction of movement of said movable member beingapproximately equal to the diameter of said convolutions plus one-halfthe distance between said first and second positions so that saidsprings roll during the entire movement of said movable member betweentheir first and second positions whereby rolling friction is encounteredbetween said members and said spring contact.

4. in electrical apparatus, current interchange means comprising a pairof conductive members, one of said conductive members being relativelyfixed and the other being movable between first and second positions,elongate channel means provided in one of said members and having itsopen side disposed adjacent the other, a helical spring contact disposedin said channel means, the depth of said channel means beingsubstantially uniform and less than the helical diameter of said springso that the convolutions thereof have their planes inclined at an anglerelative to its circumferential axis, whereby the resiliency of saidspring normally holds said convolutions in uniformly advancing spiralrelation with each other and maintains said convolutions in firmfrictional contact with said members, the Width of said channel in thedirection of movement of said movable member being approximately equalto the diameter of said convolutions plus one-half the distance betweensaid first and second positions so that said spring rolls during theentire movement of said movable member between its first and secondpositions whereby rolling friction is encountered between said membersand said spring contact.

5. In electrical apparatus, current interchange means comprising asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part of saidinternal member in concentric relation, means associated with at leastone of said members for providing an elongate channel having an openside disposed toward the other member, a helical spring contact disposedin said channel, the normal distance between said members and acrosssaid channel being substantially uniform, said distance being less thanthe outside helical diameter of the convolutions of said spring toincline said convolutions at an angle relative to the helical axis ofsaid spring so that the resiliency of said spring normally holds saidconvolutions in firm electrical contact with said members, the dimensionof said channel in the direction of relative movement exceeding thediameter of said convolutions so that said spring rolls during saidmovement whereby rolling friction is encountered between said membersand said spring.

6. In electrical apparatus, current interchange means comprising asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part of saidinternal member in concentric relation, means associated with saidmembers to provide an elongate channel having an open side disposedtoward the other member, a helical spring contact disposed in saidchannel, said channel and said spring being so arranged that a planecontaining the helical axis of said spring is perpendicular to thedirection of relative movement, the normal distance between said membersand across said channel being substantially uniform and less than theoutside helical diameter of the convolutions of said spring so that theplanes of said convolutions are inclined in an angle relative to itshelical axis, the resiliency of said spring normally holdingsubstantially all of said convolutions in firm electrical contact withsaid members, the dimension of said channel in the direction of relativemovement of said members being approximately equal to the helicaldiameter of said spring plus onehalf the distance between said first andsecond positions so that said spring rolls during the relative movementof said members whereby rolling friction is encountered between saidmembers and said spring.

7. In electrical apparatus, current interchange means Comprising astationary conductive member and a relatively movable conductive memberadjacent said stationary member, means providing an elongate channel inone of said members and having its open side disposed toward the other,a helical spring contact disposed in said channel and having asubstantially linear helical axis, said channel and said spring being soarranged that a plane containing the helical axis of spring issubstantially perpendicular to the direction of said relative movement,the depth of said channel being substantially uniform and less than theout side diameter of said spring so that the convolutions thereof havetheir planes inclined at an angle relative to its helical axis, theresiliency of said spring normally holding said convolutions in firmfrictional contact with said members, the width of said channel in thedirection of relative movement exceeding the diameter of saidconvolutions so that said spring rolls during the relative movement oflsaid members whereby rolling friction is encountered between saidmembers and spring contact.

8. In electrical apparatus, current interchange means comprising astationary conductive member and a relatively movable conductive memberadjacent said stationary member and operable between first and secondpositions, means providing an elongate channel in one of said membersand having its open side disposed toward the other, a helical springcontact disposed in said channel, the helical axis of said spring beingsubstantially linear, said channel and said spring being so arrangedthat a plane containing said helical axis is perpendicular to thedirection of said relative movement, the depth of said channel beingsubstantially uniform and less than the helical. diameter of said springso that the convolutions thereof have their planes inclined at an anglerelative to its circumferential axis, whereby the resiliency of saidspring normally holds said convolutions in uniformly advancing spiralrelation with each other and maintains said convolutions in firmfrictional contact with said members, the width of said channel in thedirection of relative movement of said members being approximately equalto the helical diameter of said spring plus one-half the distancebetween said first and second positions, so that said spring rollsduring the relative movement of said members whereby rolling friction isencountered between said members and spring contact.

9. In electrical apparatus, current interchange means comprising asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part 0E saidinternal member in concentric relation, one of said members beingaxially movable relative to the other, means associated with saidmembers to provide an elongate channel having an open side disposedtoward one of said members, a helically wound spring contact disposed insaid channel, the helical axis of said spring lying in a planesubstantially perpendicular to the direction of said axial movement, thenormal distance between said members and across said channel beingsubstantially uniform, said distance being less than the outside helicaldiameter of the convolutions of said spring to incline said convolutionsat an angle relative to the helical axis of said spring so that theresiliency of said spring normally holds said convolutions in firmelectrical contact with said members, the dimension of said channel inthe direction of relative movement exceeding the diameter of saidconvolutions so that said spring rolls during said movement wherebyrolling friction is encountered between said members and said springcontact.

10. In electrical apparatus, current interchange means comprising asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part of saidinternal member in concentric relation, one of said members beingaxially movable relative to the other and between first and secondpositions, means associated with at least one of said members forproviding a substantially annular channel having an opening toward theother member, the axis of said channel lying in a plane substantiallyperpendicular to the direction ofi. said axial movement, a helicallywound spring contact disposed in said channel, the depth of said channelbeing substantially uniform and less than the helical diameter of saidspring so that the convolutions thereof have their planes inclined at anangle relative to its helical axis whereby the resiliency of said springnormally holds said convolutions in uniformly advancing spiral relationwith each other and maintains said convolutions in firm frictionalcontact with said members, the width of said channel in the direction ofrelative movement of said members being approximately equal to thediameter of said convolutions in said direction plus one-half thedistance between said first and second positions so that said springrolls during the entire portion of said relative movement wherebyrolling friction is encountered between said members and said springcontact.

11. In electrical apparatus, current interchange means comprising asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part of saidinternal element in concentric relation, one of said members beingaxially movable relative to the other and between first and secondpositions, at least one of said members having means to provide asubstantially annular channel opening toward the other, the axis of saidchannel lying in a plane substantially perpendicular to the direction ofsaid axial movement, a plurality of helically wound spring contactsdisposed in said channel with their helical axes in substantiallyparallel relation, the normal distance between said members and acrosssaid channel being substantially uni form and less than the outsidediameter of the convolutions of each of said springs, so that saidconvolutions have their planes inclined at an angle relative to theirhelical axes, the resiliency of said springs normally holding saidconvolutions in uniformly advancing spiral relation with each other andmaintaining said convolutions in firm frictional contact with saidmembers, each of said springs being inclined in an opposite directionrelative to each spring adjacent thereto to prevent intermingling oftheir convolutions, the dimension of said channel in the direction ofrelative movement of said members being approximately equal to the sumof the diameters of the convolutions of all oil said springs in saiddirection plus onehalf the distance between said first and secondpositions so that said springs roll during the relative movement of saidmembers whereby rolling friction is encountered between said members andsaid spring contact.

12. In electrical apparatus, current interchange means including asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part of saidinternal member in concentric relation, one of said members beingrotatable relative to the other, means associated with at least one ofsaid members to provide a channel having an open side adjacent the othermember, the axis of said channel being substantially parallel to theaxis of said elements, a helically wound spring contact disposed in saidchannel, the distance between said members normal to the direction ofrelative movement and across said channel being substantially uniform,said distance being less than the outside helical diameter of theconvolutions of said spring to incline said convolutions at an anglerelative to the helical axis so that the resiliency of said springnormally holds said convolutions in firm electrical contact with saidmembers, the dimension of said channel in the direction of rotationexceeding the outside diameter of said convolutions so that the springmay roll during said rotational movement whereby rolling friction isencountered between said members and said spring contact.

13. In electrical apparatus, current interchange means having asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part of saidinternal element in concentric relation, one of said members beingrotatable relative to the other between first and second angularpositions, at least one of said members having a linear channelassociated therewith having its open side disposed adjacent the othermember, the axis of said channel being substantially parallel to theaxis of said members, a helically wound spring contact disposed in saidchannel, the normal distance between said members and across saidchannel being substantially uniform and less than the helical diameterof said spring so that the convolutions thereof have their planesinclined at an angle relative to its helical axis whereby the resiliencyof said spring normally holds said convolutions in uniformly advancingspiral relation with each other and maintains said convolutions in firmfrictional contact with said members, the width of said channel in thedirection of rotation being approximately equal to the diameter of saidconvolutions plus one-half the arcuate distance between said first andsecond angular positions, so that the spring rolls during the entireportion of said rotational movement whereby rolling friction isencountered between said members and said spring contact.

14. In electrical apparatus a current interchange means having asubstantially cylindrical internal conductive member and a substantiallycylindrical external conductive member surrounding a part of saidinternal member in concentric relation, one of said members beingrotatable relative to the other, at least one of said members having aplurality of groove means formed therein whose open side is disposedadjacent the other member, the axis of each of said groove means beingsubstantially parallel to the axis of said members and to each other, ahelically wound spring contact disposed in each of said groove meanswith their helical axes in substantially parallel relation, each of saidgrooves having a substantially uniform depth, said depth being less thanthe outside helical diameter of the convolutions of said spring toincline said convolutions at an angle relative to its helical axis sothat the resiliency of said springs normally hold said convolutions inuniformly advancing spiral relation with each other and maintains saidconvolutions in firm frictional contact with said members, the width ofeach of said grooves in the direction of rotation exceeding the outsidediameter of said convolutions so that said springs may roll during saidrotational movement whereby rolling friction is encountered between saidmembers and said spring contact.

15. In electrical apparatus a current interchange means comprising apair of relative movable conductive members having opposed relativelyplanar surfaces in close proximity, means providing an elongate channelin one of said surfaces and having its open side disposed toward theother, a helical spring contact disposed in said channel, the helicalaxis of said spring being substantially linear, said channel and saidspring being so arranged that a plane containing the helical axis ofspring is perpendicular to the direction of said relative movement, thedepth of said channel being substantially uniform and less than theoutside diameter of said spring so that the convolutions thereof havetheir planes inclined at an angle relative to its helical axis, theresiliency of said spring normally holding said convolutions in firmfrictional contact with said members, the width of said channelexceeding the diameter of said convolutions in the direction of relativemovement of said members so that said spring may roll during therelative movement of said members whereby rolling friction isencountered between said surfaces and said spring contact.

16. Contact structure for use in electric switch means comprising amovable contact and a stationary contact assembly, said stationarycontact assembly including a pair of conductive members, one of saidconductive members comprising a contact block having a recess formedtherein, the other conductive member comprising a contact fingerreceived within said recess, a channel formed in one of said members andhaving its open side disposed toward the other member, a helical springcontact disposed in said channel, the depth of said channel beingsubstantially uniform and less than the outside helical diameter of saidspring so that the convolutions thereof have their planes inclined at anangle relative to its helical axis, the resiliency of said springnormally holding said convolutions in firm frictional contact with saidmembers, the width of said channel in the direction of movement of saidother member being approximately equal to the diameter of aidconvolutions plus one-half the distance between said first and secondpositions so that said spring rolls during the movement of said othermember between said first and second positions whereby rolling frictionis encountered between said members and said spring contact.

17. Contact structure for use in electric switch means comprising amovable contact and a stationary contact assembly having a pair ofconductive members, one of said conductive members comprising a contactblock having a recess formed therein, opposite walls of said recessbeing substantially planar, the other conductive member comprising acontact finger received within said recess and having opposedsubstantially planar surfaces adjacent said opposite walls for movementbetween first and second positions, a groove formed in the planarportion of one of said members and having its open side disposed towardthe other, a helical spring contact disposed in said groove with itshelical axis substantially parallel to said planar surface and lying ina plane substantially perpendicular to the direction of said movement,the depth of said groove being less than the helical diameter of saidspring so that the convolutions thereof have their planes inclined at anangle relative to its helical axis, whereby the resiliency of saidspring normally holds said convolutions in uniformly advancing spiralrelation with each other and maintains said convolutions in firmfrictional contact with said members, the width of said groove in thedirection of movement of said contact fingers being approximately equalto the diameter of said convolutions plus one-half the distance betweensaid first and second positions so that said spring rolls during themovement of said contact finger between said first and second positionswhereby rolling friction is encountered between said members and saidspring contact.

18. Contact structure for use in electric switch means comprising amovable contact and a stationary contact assembly having first andsecond conductive means, said first conductive means comprising acontact block having a recess formed therein, opposite walls of saidrecess being substantially planar, said second conductive meanscomprising a plurality of contact fingers disposed within said recess inside-by-side relation and each having opposed substantially planarsurfaces adjacent said opposite walls, for movement between first andsecond positions, a groove formed in the planar portion of one of saidconductive means and having its open side disposed toward the other, aplurality of helical spring contacts disposed in said groove with theirhelical axes substantially parallel to each other and to said planarwalls and lying in planes substantially perpendicular to the directionof said movement, the depth of said grooves being less than the helicaldiameters of said springs so that the convolutions thereof have theirplanes inclined at an angle relative to its circumferential axis,whereby the resiliency of said springs normally hold said convolutionsin uniformly advancing spiral relation with each other and maintainssaid convolutions in firm frictional contact with said contact block andsaid contact fingers, each of said springs being inclined in an oppositedirection relative to each spring adjacent thereto to preventintermingling of their convolutions, the width of said groove in thedirection of movement of said contact fingers being approximately equalto the sum of the helical diameters of each of said springs plusone-half the distance between said first and second positions so thatsaid spring rolls during the movement of said other member between saidfirst and second positions whereby rolling friction is encounteredbetween said members and said spring contact.

l9. Contact structure for use in electrical switch means comprising amovable contact and a stationary contact assembly, said stationarycontact assembly including a pair of conductive members, one of saidconductive members comprising a contact block having a substantiallyplanar surface, the other conductive member comprising a contact fingermounted adjacent said surface for movement in a direction substantiallyparallel thereto, a groove formed in one of said members and having itsopen side disposed toward the other, a helical spring contact disposedin said groove, the distance between said members across said groovebeing substantially uniform and shorter than the outside diameter ofsaid spring so that the convolutions thereof have their planes inclinedat an angle relative to its helical axis so that the resiliency of saidspring normally holds said convolutions in firm frictional contact withsaid members, the width of said groove in the direction of movement ofsaid other member being greater than the outside diameter of saidconvolutions in the direction of relative movement of said members sothat said spring may roll during such movement.

References Cited in the file of this patent UNITED STATES PATENTS959,435 Thomson May 24, 1910 2,198,039 Onions et al Apr. 23, 19402,203,806 Wolf June 11, 1940 2,449,479 Hopper et al Sept. 14, 19482,525,730 Schulze Oct. 10, 1950 2,615,077 Tinker Oct. 21, 1952 2,965,734Timmerman Dec. 29, 1960 2,975,254 Yanagisawa Mar. 14, 1961 FOREIGNPATENTS 29,822 Great Britain June 24, 1914 186,526 Great Britain Oct. 5,1922 635,738 Germany Dec. 23, 1939 511,967 Italy Jan. 23, 1955 962,083Germany Apr. 18, 1957 1,007,576 Germany May 2, 1957

1. IN ELECTRICAL APPARATUS, CURRENT INTERCHANGE MEANS COMPRISING A PAIROF RELATIVELY MOVABLE CONDUCTIVE MEMBERS, MEANS ASSOCIATED WITH SAIDMEMBERS FOR PROVIDING AN ELONGATE CHANNEL HAVING ITS OPEN SIDE DISPOSEDTOWARD ONE OF SAID MEMBERS, A HELICAL SPRING CONTACT DISPOSED IN SAIDCHANNEL, THE NORMAL DISTANCE BETWEEN SAID MEMBERS AND ACROSS SAIDCHANNEL BEING SUBSTANTIALLY UNIFORM, SAID DISTANCE BEING LESS THAN THEOUTSIDE HELICAL DIAMETER OF THE CONVOLUTIONS OF SAID SPRING TO INCLINESAID CONVOLUTIONS AT AN ANGLE RELATIVE TO THE HELICAL AXIS OF SAIDSPRING SO THAT THE RESILIENCY OF SAID SPRING NORMALLY HOLDS SAIDCONVOLUTIONS IN FIRM ELECTRICAL CONTACT WITH SAID MEMBERS, THE WIDTH OFSAID CHANNEL IN THE DIRECTION OF RELATIVE MOVEMENT EXCEEDING THEDIAMETER OF SAID CONVOLUTIONS SO THAT SAID SPRING ROLLS DURING SAIDMOVEMENT WHEREBY ROLLING FRICTION IS ENCOUNTERED BETWEEN SAID MEMBERSAND SAID SPRING CONTACT.